Preparation of octafluorotetrahydrofuran

ABSTRACT

Disclosed is a process for the preparation of octafluorotetrahydrofuran. The process involves reacting perfluoroglutaryl fluoride with fluorine in the presence of KF, CsF, AgF or RbF as catalyst. The reaction is carried out at a temperature within the range of from about -196* to 25* C.

United States Patent Frick et al. [451 July 25, 1972 PREPARATION OF [56]References Cited OCTAFLUOROTETRAHYDROFURAN FOREIGN PATENTS ORAPPLICATIONS [72] Inventors: Hughie R. Frick; Richard W. Anderson,l138l90 12/1968 Great Britain both of Midland, Mich.

Primary ExaminerNicholas S. RIZZO [73] Assignee: The Dow ChemicalCompany, Midland, Assistant Examiner Be|-nard Demz I Mich-Attorney-Griswold & Burdick, Jerome L. .Ieffers and William 22 Filed:July 6, 1970 21 Appl. No.: 52,757 57 ABSTRACT Disclosed is a process forthe preparation of octafluorotetrahydrofuran. The process involvesreacting per- [gf] fluomglmaryl fluoride with fluorine in the presenceof KF d B46 1 R CsF, AgF or RbF as catalyst. The reaction is carried outat a [5 le o are .l temperature within the range offmm about 0 to 25C- 6Claims, No Drawings PREPARATION OF OCTAFLUORO'IETRAHYDROFURAN Theinvention described herein was made in the course of or under a contractor subcontract thereunder with the Department of the Navy.

The present invention is a process for the preparation ofoctafluorotetrahydrofuran, a composition useful as an inert solvent forhighly reactive or corrosive halogenated materials. The process is basedon the discovery that perfluoroglutaryl fluoride will react withfluorine in the presence of KF, CsF, AgF or RbF to form the desiredproduct. The reaction is carried out at a temperature of from about 1 96to 25 C.

The process is normally practiced by expanding the perfluoroglutarylfluoride into the reaction vessel containing the catalyst and coolingthe vessel to 196 C with liquid nitrogen. Fluorine is then condensedinto the vessel. Fluorine should be introduced after theperfluoroglutaryl fluoride since its vapor pressure of about 200 mm. Hgat 196 C would result in some fluorine loss were it introduced first andthe vessel reopened to introduce the perfluoroglutaryl fluoride. Thereaction proceeds at temperatures as low as about l96 C; however, as thetemperature is decreased, a more active catalyst is required. Thecatalyst becomes more active as it is used in the instantly describedreaction. Accordingly, reuse of the catalyst is desirable. The metalfluoride catalyst should be finely ground for maximum surface contact.

The maximum temperature at which the reactants should be contacted isabout 25 C. At temperatures above about 25 C fragmentation becomes thepredominant mode of reaction. Preferred reaction temperatures willdepend on the activity of the catalyst. In general, a reactiontemperature within the range of from l50 to 50 C is preferred. Thereaction is strongly exothermic. A heat transferring material such assteel wool is normally intermixed with the catalyst to preventfragmentation of the product due to overheating.

The ratio of reactants is not critical, i.e. the reaction will proceedwith an excess of either reactant. Stoichiometric amounts ofperfluoroglutaryl fluoride and fluorine are preferred since excessfluorine tends to increase product fragmentation.

Alternatively, a complex of the catalyst and perfluoroglutaryl fluorideis prepared and contacted with fluorine to form the desired product. Themetal fluoride-perfluoroglutaryl fluoride complex is prepared bycontacting these compounds in a sealed chamber at about 70 C.Preferably, the complex formation is carried out in a solvent such asB,B-dimethoxydiethyl ether, 1,2-dimethoxyethane orN,N-dimethyl-formamide. The solvent is vacuum distilled from the complexleaving a dry reactant for subsequent reaction with fluorine.Preparation of the complex permits a flow type reaction since fluorinecan be passed over and through the complexed material in a continuousmanner.

While the invention is not predicated upon the theory behind itsoperation, the following equation is believed to illustrate themechanism:

11 ll F II (il(CF2)a(3 F: FOIC(CI*Q)Q% O F F C F: C F2 00 F2 OFT-CF; Thepresence of other products such as C F ,CF -,OF and C lin the reactionvessel indicates that some fragmentation occurs.

The invention is further illustrated by the following examples.

EXAMPLE l A 25 gm. sample of cesium fluoride which had been finelyground and treated once previously with perfluoroglutaryl fluoride wasplaced in a l-liter stainless steel cylinder loosely packed with coarsestainless steel wool. A 3.22 millimole (1,143 ml. 0 52 mm. Hg) sample ofperfluoroglutaryl fluoride was condensed into the reactor at 196 C and6.44 millimole (143 ml. 0 830 mm. Hg) of fluorine was allowed to expandinto the reactor at this temperature. The reactor was closed and allowedto stand in a 78 C bath for 2.5 hours, after which time only a fewmillimeters pressure remained.

Pumping on the system through a 1 96 C trap and a sodalime trap removedsome COF and CF OF. The remaining 1.1 gm. of material was vacuumtransferred into a 30 ml. stainless steel cylinder. The material waswarmed to room temperature and shortly thereafter the contents detonatedexothermically such that a ping was heard. A subsequent infraredspectrum revealed the presence of COF and C F withoctafluorotetrahydrofuran being the major component.

EXAMPLE ll A ml. monel cylinder containing finely ground AgF was flushedwith fluorine gas and cooled to -l 96 C. Perfluoroglutaryl fluoride(0.266 gm./l .08 m. mole) was condensed to the bottom of the reactorafter which aquantitative amount of fluorine was condensed into thereactor. The reactor was closed and placed ina 55 C bath which wasallowed to warm to room temperature over a period of several hours.After a total reaction period of 20 hours the cylinder was opened andthe contents analyzed.

The contents consisted of one major product and two minor products.Analysis of the sample by gas chromatography using a 12 footperfluorotributylamine column at room temperature indicated the majorproduct to be with traces of COF and C 1 The structure of the majorproduct was confirmed by nuclear magnetic resonance.

EXAMPLE lll EXAMPLE lV Pcrfluoroglutaryl fluoride (1,143 ml. 0 52 mm. Hg3.22 m. mole) was expanded into a 1 liter stainless steel cylindercontaining 25 gm. CsF along with 5.5 gm. of stainless steel mesh.Fluorine (143 ml. 0 830 mm. Hg 6.44 m. mole) was then expanded into thecylinder and condensed. The reaction was carried outfor 3 hours. At theend of the reaction period, volatiles were vacuum stripped from thereactor at 78 C. Analysis of the products by infrared spectroscopyindicated that the major product was with traces of COP- C F and C FEXAMPLE V We claim:

l. A process for the preparation of octafluorotetrahydrofu- Cesiumfluoride (40 gm.) and 30 stainless steel balls as heat transferringmaterial were added to a stainless steel U-tube ran Y l comprisesreacung perfluoroglutaryl fluoride with fluorine in the presence of KF,CsF, AgF or RbF as catalyst at (%inch O.D. X 6 inch high) which had beenpassivated with o e fluorine. The U-tube was placed on a vacuum line forevacua- 5 a temperature wlthm the range of from about 196 to 25 C andrecovering the octafluorotetrahydrofuran.

after whlch mole of 2. The process of claim 1 wherein the reactiontemperature I H H is within the range of-from l 50 to 50 C. Y F C (0F930 F V 3. The process of claim 1 wherein the catalyst is CsF.

O 4. The process of claim 1 wherein the catalyst is finely was vacuumtransferred mm the utube at 196 The 10 ground and intermixed withaheattransferring material.

tube was warmed to 78 C and fluorine (l m. mole) was slowly pumpedthrough with the products being collected in a T prqccss of claim 4when!" the heat transfemng U t C r d f 1 h A a] f th material ISstalnlesssteel.

mp a ova a Pena 0 n ysls o e 6. The process of claim 1 whereinstoichiometric quantities g grgg gja Ea s: figfii gzfi ig amounts of l 5of perfluoroglutaryl fluoride and fluorine are reacted.

2. The process of claim 1 wherein the reaction temperature is within therange of from -150* to -50* C.
 3. The process of claim 1 wherein thecatalyst is CsF.
 4. The process of claim 1 wherein the catalyst isfinely ground and intermixed with a heat transferring material.
 5. Theprocess of claim 4 wherein the heat transferring material is stainlesssteel.
 6. The process of claim 1 wherein stoichiometric quantities ofperfluoroglutaryl fluoride and fluorine are reacted.